I would give both breeders a "heads up" after missing on the first clutch. Of course the size of the clutch will be a factor too. If you only get one or two babies from the clutch, you may not want to bother the breeders with it. If after the second clutch, still no visibles, then definitely let the breeders know. Still, be cordial and definitely don't be placing blame. Just let them know that after two clutches, nothing. If after three clutches, still no little piebalds, I'd be fairly certain that at least one parent is not a het. Be sure to explain that you really don't know which snake could be the problem. And thats something that will have to be proven before you can expect compensation. Don't assume that the one you got from "Joe Blow" has to be the problem because the other came from Bob. Joe may be (and probably is) just as honest as Bob, but everyone makes mistakes. The real problem is going to be proving which one isn't a het. I have a het piebald male and a het albino male and I may never breed either one of them for these very reasons. We have since acquired homozygous males. They can certainly prove out our het females.

Good luck!
Steve